The present invention relates to a novel fluorine-containing compound, a fluorine-containing polymer compound derived therefrom, a positive-type resist composition using the polymer compound, and a pattern forming process by the resist composition.
In recent years, throughput of operation data and of two-dimensional and three-dimensional image data has become enormous by the development of digital equipment, such as computer. In order to achieve a rapid processing of such information, there arises a demand for a high-capacity, high-speed memory and a high-performance microprocessor. Furthermore, a demand for processing ability on digital equipment is expected to become increasingly high, due to a further acceleration of broadbandization along with the development of network such as Internet.
To satisfy this demand, various devices, such as semiconductor devices, are required to have a further high-density and a further high integration. In particular, a demand for a photolithography that makes microfabrication possible has become strict year to year. For producing a DRAM having an integration degree of 1G bits or more, it is necessary to have a processing technology of a minimum line width of 0.13 micrometers or less. In response to this, a photolithography using ArF excimer laser (193 nm) is used. Furthermore, the development of a photolithography using F2 excimer laser (157 nm) is in progress for the purpose of forming fine patterns.
In these wavelength regions, it is not possible to use novolac resins and polyvinyl phenol resins, which have conventionally been used for resist compositions, since their light absorptions are too large. Thus, acrylic resins (see Japanese Patent Application Publication 10-161313) and cycloolefinic resins (see Japanese Patent Application Publication 2000-089463) have been examined.
In the case of forming patterns by using a photoresist composition, a tetramethylammonium aqueous solution (TMAH aqueous solution) is favorably used, in place of organic solvent as a developing solution, due to environmental concern. Phenolic hydroxyl group, carboxyl group, and hexafluoroisopropanol group are known as functional groups that are soluble in TMAH aqueous solution, that is, functional groups that make a development by TMAH aqueous solution possible. In the case of using wavelengths of ArF (193 nm) and F2 (157 nm), aromatic ring has intense absorption bands at the both wavelength regions. Therefore, carboxyl group or hexafluoroisopropanol is mainly in examination. In the case of forming particularly fine patterns, resins having a hexafluoroisopropanol group provide resist compositions that are superior in transparency, development property, and adhesion to substrate, thereby providing relatively good patterns. It is, however, known that a special synthesis technique is necessary for forming those resins. On the other hand, resins having a carboxyl group as the functional group swell in TMAH aqueous solution. Therefore, it is difficult to obtain patterns as originally designed (see Japanese Patent Application Publication 2007-086514).
As carboxylic compounds having a fluorine atom at α-position, 2-fluorophenylacetic acid and its ester (see Japanese Patent Application Publication 1-242551) and ethyl 2,2-difluoro-3-hydroxy-3-phenylpropionate (see Tetrahedron Letters, Vol. 25, No. 22, pp 2301-2302, 1984) are known.